进行润色：When calculating gradient of the velocity model it is still possible to base them on the acoustic assumption This is because the size of the gradient depends only on the magnitude of the waveform

When calculating the gradient of the velocity model, it is possible to base it on the acoustic assumption. This is because the size of the gradient depends only on the magnitude of the waveform perturbation in the backward residual source. The amplitude of the wavefield is a coefficient that can be corrected by the iterative step size in the calculation.